Cut-off knife for corrugators

ABSTRACT

A cut-off knife for corrugators with at least one rotating knife bar for subdividing a web into sheets to which driving rotary motion is provided by a variable adjustable speed control gear and by a subsequently connected differential gear wherein the adjusting mechanisms of the speed control gear and the differential gear are not mechanically connected with one another. The control range of the speed control gear is subdivided into individual sections with each section producing a nominal-value signal; the differential gear is adjusted to provide an actual-value signal for each adjustment. The difference between the nominal and the actual value signals form an output signal that controls the adjustment of the differential gear until the actual-value signal matches the nominal-value signal. The adjustment of the differential gear is preferably automatically controlled with the aid of the difference between the nominal-value signal and the actual-value signal so that the knife speed can be conformed to the speed of the web of material during operation.

[11] 3,826,169 .1 July 30,1974

United States Patent [191 Schnell et al.

[ l CUT-OFF KNIFE FOR CORRUGATORS [75] Inventors: Gunter Schnell, Bochum; Klaus ABSTRACT A cut-off knife for corrugators with at least one rotat- Albert Hohage,l-lattingen (Ruhr), ing knife bar for subdividing a web into sheets to both of Germany which driving rotary motion is provided by a variable adjustable speed control gear and by a subsequently [73] Asslgnee' goppers Company Pmsburgh connected differential gear wherein the adjusting mechanisms of the speed controlv gear and the differ- [22] Filed: Aug. 3, 1973 ential gear are not mechanically connected with one another. The control range of the speed control gear is [2]] Appl 385287 subdivided into individual sections with each section producing a nominaLvalue signal; the differential gear is adjusted to provide an actual-value signal for each adjustment. The difference between the nominal and the actual value signals form an output signal that controls the adjustment of the differential gear until the actual-value'signal matches the nominal-value signal. The adjustment of the differential gear is preferably automatically controlled with the aid of the difference between the nominal-value signal and the actual-value signal so that the knife speed can be conformed to the speed of the web of material during operation.

7 Claims, 4 DrawingEigures 404 4 747 XXXX 49943 31 2992 d? names 3333 4 8888 B9 n u "n w M 8 m4 B m mm 2 m mm muB N n an "M3 E m mm "8 T "0. A m m m .nP m mmm mmm CS ew m" E eme C r nn Mn" n w mvnm u E O e... an T nh .n a SUTMDS uh 9.0 R un B73355 w 36666 "S MUN/WWW 2 444 S .M in. I 69975 UImF 89756 2 1 I 66 111 1 .N M 218 6 0111 5.5.5 1 2 3 3 33 Primary Examiner-Frank T. Yost Attorney, Agent, or Firm-Olin E. William; Oscar B. Brumback; Boyce C. Dent PATENTED JULBO I974 SHEET 10F 4 PATENTED JUL 3 01914 sum 2 or 4 PATENTED JUL 3 0 I974 sum 3 or 4 PAIENIEU JUL301974 SHEEHHIF 4 1 CUT-OFF KNIFE FOR CORRUGATORS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to cutting where the cutting motion of the tool has a component in the direction of moving work and more particularly with means to concurrently adjust the flying frequency and retain the flying speed of the tool.

' 2. Description of the Prior Art In conventional cut-off knives the function of the speed control gear is to drive the rotary knives of the cut-off at a speed at which the ratio of the web speed to the rotary speed of the knife is equal to the length of the sheet to be separated from the web. The differential gear, on the contrary, provides for synchronism of the knife with the web of material to be cut. Exact synchronism between the knife and the web of material is seldom attained in practice. For a clean separation of the individual sheets from the web of material it is sufficient when the web speed and the knife speed have about the same value, i.e., a value at which a stretching of web material during the cutting operation is below the tensile strength of the material to be cut or a bulging of the web of material by the knife does not result in a change of the level position of the web of material. To simplify the operation of a rotary cut-off knife, the adjusting mechanisms of the speed control gear and differential gear have been mechanically connected with one another so that both gears can be adjusted simultaneously and thus dependently. As a result of this,-the adjustment of the differential gear must follow the adjustment of the speed control gear, i.e., the length of the sheet. However, since no linear dependence exists between the length of the sheets and regulation of the synchronism of the differential gear formed as a double crank gear, the knife and web usually run at exactly the same speed only in one position, i.e., where their characteristic curves touch and cut, respectively, whereas in the remaining part of their range of adjustment their speed considerably variesfrom one another. But, to be able to adapt the knife speed at all speeds of the speed control gear to the speed of the web of material, the adjustment of the differential gear has usually been separated from the adjustment of the speed control gear resulting in inaccuracies in cut length of the sheet.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention gen erally is to provide a cut-off knife for subdividing material in the form of webs, such as paper, paperboard, or plastic, to which driving rotary motion is supplied by a variable adjustable speed control gear, or so-called format gear, and by a subsequently connected differential gear wherein the speed control gear and the differential gear are not mechanically connected with one another. More specifically, an object is to control the differential gear in a rotary cut-off knife in which the adjusting mechanism of the speed control gear and the adjusting mechanism of the differential gear are not mechanically connected with one another so that the knife speed matches the speed of the web of material at all rotary speeds of the knife.

These and other objects are achieved by providing a cut-off knife with at least one rotating knife bar for subdividing material in the form of webs to which, driving rotary motion is imparted by a variably adjustable speed control gear and by a subsequently connected differential gear wherein the adjusting mechanisms of the speed control gear and the differential gear are not mechanically connected with one another. A control range of the speed control gear is divided into individual sections and each section produces a nominal-value signal; the differential gear is adjusted to provide an actual-valuesignal for each adjustment. The difference between the nominal and the actual value signals form an output signal that controls the adjustment of the differential gear until the actual-value signal matches the nominal-value signal. The adjustment of the differential gear is preferably automatically controlled with the aid of the difference between the nominal-value and the actual-value signals so that the knife speed can be adapted to the speed of the web of material during operation.

The above and further objects andnovel features of the invention will appear more fully from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like parts are marked alike:

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred construction of the invention, exact synchronization between the cutter and the web of material is not absolutely necessary since an approximation of both speeds within specific limits is sufficient to obtain a square and clean cut; thus, the differential gear may be adjusted in steps. With a stepwise subdivision of the adjusting range and the coordination of the individual adjusting ranges to one of the speed ranges of the variable and adjustable speed control gear with the aid of the difference between the nominal value and the actual value, it is possible to exclude substantial fluctuations of the characteristic curves of both gears, such as those that cannot be avoided in a mechanical coupling of the adjusting mechanisms of both gears. Coupling of both gears is attained in this manner and makes it possible for an operator to adjust the differential gear simultaneously with corresponding adjustment of the speed control gear. This was previously possible only in case of separate adjustment of the speed control gear and the differential gear. This results in more rapid adjustment of the cut-off knife and resultant reduction of waste and also simplifies the control of the length of the cut sheets since their length is controlled solely by the speed control gear. This also lengthens the life of the adjusting mechanism that is subject to high stress caused by high inertia forces of the cutter bars.

Preferably, the cut-off is equipped with a stepping switch device coupled to the speed control gear which provides the nominal-value signal in cooperation with a resistance network; moreover, it may also include a series parallel potentiometer coupled with a differential gear to provide the actual-value signal; and it may also include a differentiating amplifier to transform the nominal-value signal and the actual-value signal to an output signal which acts on a control or servomotor of the differential gear by a control network, although the definite nominal-value signal coordinates the stepping switch to each individual speed range of the speed control gear; the actual-value signals supplied to the differentiating amplifier together with the nominal-value signal are formed by the individual switching steps of the differential gear with the aid of the series parallel potentiometer. The output signal of the differentiating amplifier also assures that the best single stage of the differential gear takes place for each speed range of the speed control gear, i.e., a single stage at which the difference between the nominal-value and the actualvalue is zero. I

The stepping switch of the speed control gear may be in the form of a conventional multiple-contact camshaft controller. With such a controller, the entire operating range of the speed control gear can be easily subdivided into individual sections which provide an output signal from the stepping switch.

As will be later explained in greater detail, the differential gear is suitably equipped with a stop that locks it in its individual operating positions and disengages the servomotor. This stop is controllable together with the differential gear and is formed as a clamp that braces the control mechanism and, in addition to the servomotor, also disengages the control mechanism of the differential gear from the high inertia forces generated by the cutter bars thereby reducing wear of the gear components.

Alternatively, the knife speed can be adapted to the speed of the web of material by designing the differential gear as a rotating crank slide. The characteristic curve of such a differential gear has a course similar to that of the characteristiccurve of the speed control gear so that the difference in speed between the web of material and the knife is particularly low when used in connection with a stepwise subdivision of the adjusting range of the differential gear.

Referring now to FIG. 1, a web of corrugated paper A moves at substantially constant speed between the two knife or cutter bars 1 and 2 each of which is provided with a knife 3 extending over the length of the bars. Both knife bars 1 and 2 are connected with one another so that they can be driven together by a pair of conventional gears (not illustrated) to rotate in opposite directions as shown by arrows 4. The moving web of paperboard A is cut into individual sheets whose length is determined by the quotients of the web speed and the number of revolutions of the knife bars. To obtain a clean cut at a right angle to the direction of motion of the web of corrugated paperboard, the web speed and the knife speed must approximately agree during the cutting operation. Consequently, when short sheets are produced, the angular speed of the knife bars 1 and 2 rotating at high speed must be reduced during the actual cutting operation and, when long sheets are separated, the angular speed of the two knife bars 1 and 2 rotating a low speed must be accelerated during the cutting operation. This constant synchronization of the rotational speed of the knife bars 1 and 2 to the speed of the web to be cut is effected by the differential gear 5 which is designed as a double crank gear in FIG. 1.

The rotary motion for the cutter bars 1 and 2 is initiated, reduced, and supplied to shaft 8 of the differential gear 5 by output shaft 44 of a conventional variable, adjustable speed control gear 7 illustrated in block form in FIG. 1. This rotary motion is then transmitted by a pinion 9 to the internally toothed wheel 10 of the differential gear 5 along the periphery of which the coupling link 12 is pivotally secured by pin 11. On the opposite end of link 12, pin 13 articulately couples link 12 with the crank arm 14. The opposite end of crank 14 is connected for rotation with the shaft 15 of the lower knife bar 2. The hub 16 of the internally toothed wheel 10 is supported rotatably on the pin 17. The latter is held by the adjusting disk 18 which is situated eccentrically in relation to the shaft 8 of the differential gear 5.

The control motion is initiated in the equalizing gear 5 by means of a worm 19 that engages corresponding worm gear teeth on a control disk 18. A conventional servomotor 20 turns the control disk 18 about the shaft 8 and thereby rotates the pin 17 carrying the wheel 10 at an angle. Consequently, the frame length of the differential gear 5, which is determined by pin 17 and shaft 15, is changed; the degree of irregularity of the differential gear is also varied with it. With correct adjustment of the control disk 18, the rotary motion of the speed control gear 7 is always transferred to both knife bars 1 and 2 with the aid of the differential gear so that the knives 3 are moved at a rotary speed that corresponds to the speed of the web during the actual cutting operation.

A clamp device 21 consisting of two clamp segments 21A and 21B hinged by pin 21C surround a portion of collar 22 of the control disk 18. Clamp 21 is operated by a lever rod 23 connected to a hydraulic cylinder 25 held at 24. Cylinder 25 urges clamp segments 21A and 218 against collar 22 when the control motion of the disk 18 is to be stopped. Thus, in its locked position, the clamp device 21 stops the adjusting mechanism. It thereby supports the control disk 18, disengages its seating, and prevents a stress on the adjusting mechanism and on the servomotor 20 by the resultant reaction forces in case of a constant acceleration or deceleration of both knife bars 1 and 2.

As illustrated in the example of FIG. 2, the differential gear 5 can also be constructed as a revolving crank slide. The crank 26 is secured for rotation with the shaft 15 of the lower knife bar 2 and its free end slides in a guide 27 which is rotatably mounted by pin 11 on the periphery of theinternally toothed wheel 10. Crank 26 runs at variable angular speed upon each revolution of the uniform rotation of the wheel 10 and adapts the peripheral speed of the knife 3 in the cutting range to the speed of the web of material to be subdivided. Since the characteristic curve of differential gear 5 in connection with a revolving crank slide comes closer to the characteristic curve of the speed control gear 7 than does the characteristic curve of the differential gear 5 in connection with a double crank gear as shown in FIG. 1, closer synchronization between web speed and knife speed is obtained with the crank slide, particularly in the peripheral zones of the control range.

As illustrated in the block diagram of FIG. 3, the speed control gear 7 is also equipped with a conventional servomotor 28 coupled to a well known stepping switch 29. The servomotor 28 is operated manually by a format adjuster 30 with the aid of control 31 to adjust the output speed of speed control gear 7 so that both knife bars 1 and 2 revolve at a speed at which the ratio of the web speed to the knife speed gives the desired cut length (length of sheet). Depending on the number of revolutions of servomotor 28, the stepping switch 29 produces a nominal-value voltage in a resistance network 32; the nominal-value voltage flows to the differentiating amplifier 33. The differentiating amplifier 33 also receives an actual-value voltage which is formed with the aid of a well-known series parallel potentiometer 34. Since the servomotor 20, which brings the differential gear 5 into the correct operating position (FIGS. 1 and 2) by means of the worm l9 and the control disk 18 and which is coupled with the series parallel potentiometer 34, the actual-value voltage prevailing before the differentiating amplifier 33 always produces the particular adjustment of the differential gear 5 i.e., the double crank gear or the revolving crank slide. If the nominal-value voltage and the actual-value voltage do not conform, the output voltage of the differentiating amplifier 33 readjusts the differential gear 5 by means of the servomotor 20. When this difference between the nominal-value and the actual-value diminishes, i.e., when it is zero, the control 35 disconnects the servomotor from the main supply line 36. The differential gear 5 is immediately clamped in precise position by the clamping device 21.

As illustrated in FIG. 4, an automatic adjustment 37 may be substituted for manual control 30 to include conventional individual decade switches a, b, c, and d, which form the standard formats and adjusts them in ranges of meters, decimeters, centimeters, and millimeters or equivalent dimensions. These switches act on a differentiating amplifier 39 through a resistance network 38. The nominal-value voltage is determined by network 38 and flows to the differentiating amplifier 39 where it is actuated and compared with an actual-value voltage determined by the speed control gear 7; the resultant difference between the nominal-value and the actual-value is used for operation of a control 40 rotate a servomotor 41 in the correct direction of rotation. The quotient of the voltages of two tachometergenerators 42 and 43, which are coupled respectively with the drive shaft 6 and with the drive shaft 44 of the speed control gear 7, provides an actual-value voltage. Since the drive shaft 6 receives its rotary motion from the drive for the heating and cooling parts of a corrugated paperboard machine (not illustrated), the actualvalue formed by the quotient of both tachgenerators 42 and 43 is independent of fluctuations or changes of the speed of the web A of corrugated paperboard. The nominal-value voltage necessary to adjust the speed control gear is used to adjust the differential gear 5. In the example of FIG. 4, the decade switches a, b, and c, which adjust the lengths of the sheets in the ranges of meters, decimeters, and centimeters, are connected through the resistance network 32 to the differentiating amplifier 33. Since the control need only provide a substantial synchronization of the knife speeds to the web speed, it is possible-to omit the connection of decade switch d, which adjusts the length of the sheets in millimeters, and also omit the resistance network 32 and the differentiating amplifier 33. Otherwise, the control operates as in the previously described example of FIG. 3; therefore, the servomotor 20 rotates in the proper direction by virtue of the signal transmitted from the differentiating amplifier 33 by the control 35 and the adjustment of the differential gear 5 is corrected as long as the output voltage of the series parallel potentiometer 34 has been synchronized to the nominal-value voltage.

Accordingly, the invention having been described in its best embodiment and mode of operation, that which is desired to be claimed by Letters Patent is:

1. A cut-off knife including at least one rotatable cutter knife bar for cutting a web of paperboard into individual sheets comprising:

a variably adjustable gear means including a selectively operable first adjustment means for adjusting an output of said adjustable gear means to drive said knife bar at a substantially constant speed corresponding in proportion to the length of said sheets to be cut from said web, said first adjustment means including a plurality of individual control sections each producing a nominal-value voltage signal corresponding to the sheet length selected;

an adjustable differential gear means coupled between said variably adjustable gear means and said knife bar including an automatically operable second adjustment means for adjusting said differential gear means independently of said first adjustment means to accelerate or decelerate said knife bar to a speed substantially corresponding to the speed of said web during cutting thereof, said second adjustment means producing an actualvalue voltage signal corresponding to the speed of said knife bar during cutting of said web; and

a control network responsive to a difference between said nominal and actual-value voltage signals for automatically adjusting said differential gear means through said second adjustment means until said signals substantially correspond in value.

2. The cut-off knife of claim 1 wherein:

said first adjustment means comprises stepping switch means coupled to said variably adjustable gear means and to a resistance network for producing said nominal-value voltage signal;

said second adjustment means includes a series parallel potentiometer means coupled to said differential gear means for producing said actual-value voltage signal; and

said control network includes a differentiating amplifier means responsive to said nominal and actualvalue voltage signals for producing a corrective output signal; and in addition,

servomotor means coupled to said second adjustment means and responsive to said output signal for adjusting said differential gear means.

3. The cut-off knife of claim 2 wherein:

said first adjustment means comprises decade switch means coupled to said variably adjustable gear means and to a resistance network for producing said nominal-value voltage signal.

4. The cut-off knife of claim 2 further including:

stop means for clamping said differential gear means in an operating position corresponding to a substantially zero difference in value between said said differential gear means includes articulated crank means connecting said differential gear means to said knife bar.

7. The cut-off knife of claim 1 wherein:

said difierential gear means includes crank slide means connecting said differential gear means to said knife bar. 

1. A cut-off knife including at least one rotatable cutter knife bar for cutting a web of paperboard into individual sheets comprising: a variably adjustable gear means including a selectively operable first adjustment means for adjusting an output of said adjustable gear means to drive said knife bar at a substantially constant speed corresponding in proportion to the length of saiD sheets to be cut from said web, said first adjustment means including a plurality of individual control sections each producing a nominal-value voltage signal corresponding to the sheet length selected; an adjustable differential gear means coupled between said variably adjustable gear means and said knife bar including an automatically operable second adjustment means for adjusting said differential gear means independently of said first adjustment means to accelerate or decelerate said knife bar to a speed substantially corresponding to the speed of said web during cutting thereof, said second adjustment means producing an actual-value voltage signal corresponding to the speed of said knife bar during cutting of said web; and a control network responsive to a difference between said nominal and actual-value voltage signals for automatically adjusting said differential gear means through said second adjustment means until said signals substantially correspond in value.
 2. The cut-off knife of claim 1 wherein: said first adjustment means comprises stepping switch means coupled to said variably adjustable gear means and to a resistance network for producing said nominal-value voltage signal; said second adjustment means includes a series parallel potentiometer means coupled to said differential gear means for producing said actual-value voltage signal; and said control network includes a differentiating amplifier means responsive to said nominal and actual-value voltage signals for producing a corrective output signal; and in addition, servomotor means coupled to said second adjustment means and responsive to said output signal for adjusting said differential gear means.
 3. The cut-off knife of claim 2 wherein: said first adjustment means comprises decade switch means coupled to said variably adjustable gear means and to a resistance network for producing said nominal-value voltage signal.
 4. The cut-off knife of claim 2 further including: stop means for clamping said differential gear means in an operating position corresponding to a substantially zero difference in value between said nominal and actual-value voltage signals and for disconnecting said servomotor means from an energy source for said servomotor means.
 5. The cut-off knife of claim 4 wherein: said stop means braces said second adjustment means against inertial forces imposed thereon by acceleration and deceleration forces from said rotating knife bar.
 6. The cut-off knife of claim 1 wherein: said differential gear means includes articulated crank means connecting said differential gear means to said knife bar.
 7. The cut-off knife of claim 1 wherein: said differential gear means includes crank slide means connecting said differential gear means to said knife bar. 